This is a continuation application of United Kingdom application 9913567.5 filed in the U.K., Jun. 11, 1999, now pending. Priority is claimed to PCT application No. GB 99/04097 filed Dec. 10, 1999.
This invention relates generally to handling of waste materials especially particulate solids. A method of transferring such materials from one location to another, and an apparatus suitable for performing the method, is described hereinafter. The invention finds particular utility in the oil and gas industry for disposal of well or drill cuttings (xe2x80x9chereinafter cuttingsxe2x80x9d) discharged from the solids control system on a well drilling site.
Cuttings are typically pieces of rock, which have been chipped, ground or scraped out of a formation by a drill bit. Various types of drill cutting tools_are in use for this purpose and the invention hereinafter described is not limited to use of any particular type.
The drilling operation is conducted several hundred meters below the operation control point, which means that performance of the drill bit is critical to the operation. The effectiveness of the drill bit during a drilling operation relies upon the continual removal of cuttings; otherwise the drill would rapidly foul up due to accumulation of cuttings. Therefore, the cuttings are normally removed by delivery of a drilling fluid (often referred to as xe2x80x9cdrilling mudxe2x80x9d) down to and around the drill bit in a recirculated manner by use of the drill string and annulus casing well established in the industry.
Accordingly the cuttings are commonly separated from the drilling fluid by devices such as a shale shaker, which captures cuttings and large solids from the drilling fluid during the circulation thereof. Basically, such a device has a sloping, close mesh, screen over which fluid returning from the hole being drilled passes. The screen may be typically of from 200xc3x97200 down to 30xc3x9730 mesh and is vibrated to facilitate separation of the majority of fluids from the solids. The solids captured on the screen travel down the sloping surface to be collected in the shaker ditch or cuttings trough. It is also desirable to recover as much of the expensive drilling fluids as possible. Therefore, other devices, which play a role in the separation of solids from drilling fluids, include cyclone separators, and centrifuges. The cuttings discharged from the shakers, cyclone""s and centrifuges that are collected in the shaker ditch or cuttings trough are still highly contaminated with the drilling fluids and therefore form a slurry or heavy sludge. The slurry or sludge is very difficult to move or otherwise transfer in any conventional manner.
In some cases the cuttings slurry may be discharged directly into a cuttings box where space permits or vacuum collected, which under current practice means that the cuttings are sucked from the cuttings ditch or trough, by an applied vacuum, directly into a cuttings box for transport to an approved disposal site for re-claimation suggested in GB-A-2 286 615. However, in some cases in order to facilitate removal of the cuttings, a collection hopper may be used which allows a particular ground clearance typically of about 4 meters whereby the cuttings are discharged from the hopper by free-fall into open cuttings containers.
It is also proposed there to include another trough for intermediate collection of cuttings. A screw conveyor for lateral displacement of cuttings from beneath the intermediate trough is described. The screw conveyor pushes the cuttings, which fall into it from the trough towards a discharge trap door that opens under the weight of the cuttings to periodically allow the cuttings to fall into the holding tank.
The intermediate trough described remains under the influence of the suction pump to continue delivery of recovered fluid to a recycle system, whilst the screw conveyor below the trough shifts cuttings towards the trap door.
In a more recent operational system a vacuum cuttings hopper is provided including, a helical screw therein on a vertically arranged shaft driven by an overhead motor assists the delivery of the solids to the free-fall outlet for collection below the hopper, The cuttings are further subjected to compression by the helical screw prior to discharge thus extracting and recovering a substantial amount of the remaining fluids in the slurry. The extracted fluid is then withdrawn through a perforated casing around the screw under the action of a pump.
The problems associated with cuttings handling for disposal are familiar to all workers on a drilling installation and include the need for the presence of several storage containers to handle the volumes of cuttings produced and the time demands upon the installation""s crane devoted to the shifting of a filled container to substitute an empty container close to the shaker station. This container xe2x80x9cshuttlingxe2x80x9d routine is not only absorbing useful operational time for the crane but also presents additional physical hazards to workers involved in other tasks in close proximity to the cuttings containers. Furthermore, the cuttings recovery equipment and the containers themselves are usually accessed by workers scaling ladders, or scaffolding or the like staging up to heights often approaching 5 or 6 meters or thereabouts in order to open container lids or service the cuttings handling equipment. Of necessity the containers themselves must be sited close to the cuttings shaker station and be accessible by the crane. These factors have an impact on use of deck space, personnel mobility, and other task completion operations around the deck.
Further the filling and relocation of cuttings containers is dictated by the volume of cuttings being produced by the drilling operation in any given period of time. Therefore, it is essential that the cuttings handling apparatus and its methods of operation be capable of handling the volumes required to maintain production.
An object of the present invention is to provide improvements in cuttings handling for disposal and recovery of reusable drilling fluids and muds from the drill cuttings slurry thereby reducing cost of disposal and recycling. A
object fulfilled by aspects of the invention to be described hereinafter is to provide a drill cuttings recovery system of more compact or efficient design.
A still further object is to provide a more flexible disposal method allowing the operator greater degree of freedom in the options for handling the cuttings prior to disposal.
Generally the invention seeks to provide a system and method for handling of cuttings, which offers an improved alternative to current handling systems.
The invention, according to a first aspect, provides a method for handling cuttings that includes providing a system utilizing a screw pump to remove the cuttings from the cuttings trough and disperse them through a piping system to various disposal points.
The invention according to another aspect, provides a method for handling of cuttings, which method comprises providing a vessel adapted to sustain a reduced internal pressure with respect to external ambient atmospheric pressure, and external pumping means, said vessel and pumping means being operationally connected by means including a conduit, collecting cuttings from a drilling fluid/cuttings separation device in said vessel, removing cuttings from said vessel by means of said pumping means through said conduit whilst maintaining a reduced pressure, and selectively delivering removed cuttings by means of pumping to at least one of a variety of disposal points including a cuttings re-injection apparatus, removable transportable cuttings containers including a barge or the like for shipping to a remote disposal site.
According to another aspect of the invention there is provided an apparatus for handling of cuttings, comprising a vessel adapted to sustain a reduced internal pressure with respect to external ambient atmospheric pressure, and further provide a means for extracting fluids, the apparatus also having operationally connected thereto, external pumping means capable of maintaining the reduced internal pressure and removing the separated fluids while discharging the cuttings to a variety of storage containers or to a cuttings re-injection apparatus.
In accordance with still another aspect of the invention a centrifugal dryer is provided for drying the drill cuttings prior to distribution, by way of a blowers and or vacuum systems, to various holding containers located on or near the rig. This drying process removes the fluids and thereby allows all of the cuttings being produced by the drilling operation to be contained on the rig for longer periods of time prior to removal or re-injection.
Significantly, according to the invention, the proposed use of the pumping means for not only initially collecting the cuttings under vacuum, but also removing cuttings under reduced pressure or xe2x80x9cvacuumxe2x80x9d conditions, and utilizing the pumping means to selectively convey the cuttings onwards via dedicated conduits to a cuttings storage container, or directly into a cuttings re-injection facility, offers several significant advantages.
Firstly, the demands on the crane are reduced because the cuttings containers do not need to be continually cycled around for filling and emptying operations. The containers can be stowed or sited in convenient locations without taking account of the shaker station position other than to ensure that suitable vacuum conduit lines are available or provided to feed the cuttings directly into the containers. The crane then becomes essentially free to fulfill other essential tasks such as handling drill pipe etc. The freedom to locate containers anywhere that a cuttings vacuum transport line can be installed and accessed immediately also provides greater freedom on the deck for operator movement, and greater flexibility in utilization of deck space around the shaker station and elsewhere.
Secondly it offers the possibility of directly off-loading cuttings to a barge or bulk transport ship standing on station close to the drilling facility.
Thirdly, health and safety aspects are enhanced due to reduced contact between workers and the cuttings, who need longer clamber over the cuttings containers to access them thereby reducing contamination hazards and risks of personal injury by falls.
The conduit network may be a fixed installation or arranged so as to permit re-deployment of a selected or each conduit at will. The conduits are designed sufficiently to permit transfer of the particulate solids constituting the cuttings and avoid blockages, and pump overloading but are also sized to avoid loss of vacuum transfer velocity.
It will be understood that the pumping means referred to herein in relation to the various aspects of the invention may consist of one or more pumps having the necessary functions of generating a pressure differential to move cuttings in the desired way and combinations of pumps can be adopted.
Preferably, the pumping means comprises, at least, (i) gas pumping means e.g. a vacuum generating unit capable of creating the desired pressure reduction in the vessel and (ii) a solids displacement means, which may be one of several types suitable to the purpose, including positive displacement pumps, e.g. a piston pump, or paddle devices e.g. using rubber paddles, or a progressive cavity pump capable of continuous displacement of solids, preferably at about 25 tons per hour or more. Advantageously, location of the pumping means external to the vessel is such that solids displacement is so primarily lateral rather than vertical as required for the known solids free-fall under gravity system, which reduces height requirements The vessel can then be installed at ground (deck) level with no height elevation requirements which improves safety for operatives.
In this way equipment provided in accordance with the invention can exhibit a relatively low profile compared with prior art systems and is more easily installed and maintained by operatives with less risk of injury due to falls. Furthermore in contrast with the prior art operational system described above where the vertically arranged helical screw is within the cuttings hopper itself, the pressure vessel arrangement described herein is less complicated in structure and provides for easier care and maintenance operations.
Overall, the system proposed herein results in more efficient use of space in the installation, and reduces hazards associated with earlier systems.
The vessel and pumping means described herein are operationally connected so as to maintain a reduced pressure or vacuum within the system, which may be achievable by fastening arrangements satisfying usual industry pressure vessel standards, including flanged connections and dedicated hard conduits of adequate strength. The reduced pressure can be maintained by a suitable type pump known in the industry or custom built for this system.
It will be understood that primarily the invention addresses solids handling, and the precise nature of the vacuum unit or gas pump is not critical. The arrangement of the invention is such that the pumped cuttings can either be directed from the reduced pressure vessel into appropriate storage facilities such as containers or directly into a cuttings re-injection device enabling the cuttings to be returned to the drilled formation. Furthermore the cuttings can be xe2x80x9cpipedxe2x80x9d off the installation into a barge or similar bulk cargo transporter.
Cuttings re-injection under high pressure back into an earth formation is described in principle in the following U.S. Pat. Nos. 4,942,929, 5,129,409, and 5,109,933, and treatment of drill cuttings is discussed in the following U.S. Pat. Nos. 4,595,422, 5,129,468, 5,361,998 and 5,303,786. However, these early proposals have not been easy to implement in the field for those lacking the appropriate skill and understanding, and this has resulted in cuttings re-injection not gaining wide acceptance amongst operators, especially in offshore drilling installations in the North Sea.
The present invention arises from developments following on from proven re-injection techniques successfully employed by APOLLO Inc. in offshore drilling operations.